1. Field of the Invention
This invention relates to coated articles and processes therefor, more particularly to articles coated with a copolymer of 3,3,3-trifluoro-2-trifluoromethyl propene and vinylidene fluoride.
2. Discussion of the Prior Art
Coating compositions of fluoropolymers, such as those based on polytetrafluoroethylene, have been used for some time to provide non-stick and protective surfaces on substrates, especially metal substrates. For example, cookware (such as frying pans, etc.), steam iron sole plates, industrial drier rollers and other articles have been coated with polytetrafluoroethylene compositions and have met with great acceptance by consumers and industry. However, such coated articles are susceptible to scratching and abrasion and hence the coated surfaces must be handled carefully. Moreover, it is necessary in the commercial production of coated cookware to utilize a primer coat of the grit type on the metal substrate prior to coating with the fluoropolymer. It would be desirable if metal substrates could be provided with a fluoropolymer surface that is abrasion and scratch resistant and does not require an intermediate primer coat.
Copolymers based on 3,3,3-trifluoro-2-trifluoromethyl propene and vinylidene fluoride are described in U.S. Pat. No. 3,706,723 to Chandrasekaran et al. Such copolymers have high melting points, good thermal stability and are resistant to attack by corrosive agents. U.S. Pat. No. 3,706,723 describes such copolymers as suitable for making a wide variety of useful products, such as coatings (e.g., protective coatings). However, it has been found that when such copolymers are coated on a metal substrate in relatively thick layers by a powder coating technique and allowed to "flow out" at elevated temperatures, surface microcracks in the coating layer appear. Surface defects such as microcracks are especially undesirable in coatings which are intended to afford protection from corrosive agents as well as in the other areas of use.